Rectifying system



Jan.- 30, 1951 A. Lyssa/IAN 2,539,786

' RECTIFYING SYTEM Filed May 27, 1946 POWER SUPPLY VOLTAGES COMMUTAT & N6

V0 LTAG ES Patented Jan. 30, 1951 RECTIFYING SYSTEM Marcel A. Lissman,Cambridge. Mass., assignor to Raytheon Manufacturing Company, Newton,Mass, a corporation of Delaware Application May 27, 1946, Serial No.672,468

2 Claims.

This invention relates to rectifying systems for multi-phase,alternating-current power supplies, and more particularly to rectifyingsystems of the general character indicated which include gridcontrolled,gaseous-discharge tubes, commonly known as thyratrons.

An object of the present invention is to provide such rectifying systemswith simple and efficient means for obtaining a continuously variableoutput voltage.

Another object of the present invention is to provide such rectifyingsystems with means for protecting the same against possible .damage bythe inverse voltages of the power supply.

These and other objects of the present invention, which will become moreapparent as the detailed description thereof progresses, are attained,briefly, in the following manner:

The system contemplates the provision of a plurality ofgaseous-discharge tubes each of which includes a cathode, an anode, anda control grid, said tubes having their anode-cathode and grid-cathodecircuits so connected, in phase opposition, to a multi-phase,alternating-current power supply to be rectified as to be initiallynon-conducting. A load impedance is connected in series with thepotential difierence applied between the anodes and cathodes of saidgaseousdischarge tubes, and means are provided for shifting the initialphase of the potential difierence applied between the control grids andcathodes of said tubes, whereby said tubes become successivelyconducting, each for a time interval, the duration of which is afunction of the magnitude of said phase shift. The conducting state ofeach of said gaseous-discharge tubes causes a current to flow throughsaid load impedance. and the average potential developed across saidload impedance is a function of the duration of said time interval.Thus, by adjusting the magnitude of said phase shift, the magnitude ofthe output voltage can be controlled between zero and the maximum ofwhich the system is capable.

The system also contemplates the provision of a second group ofgaseous-discharge tubes, each of which includes a cathode and an anode,this second group of tubes being connected, respectively, in series withthe tubes of the first abovementioned group. The arrangement is suchthat the anodes of said first-named gaseous-discharge tu es. c n n v rso s neg tiv with respect o their corresponding cathodes as to subjectsaid tubes to damaging inverse voltages.

In the accompanying specification there shall be described, and in theannexed drawings shown,

an illustrative embodiment of the rectifying system of the presentinvention. It is, however, to be clearly understood that the presentinvention is not to be limited to the details herein shown and describedfor purposes of illustration only, inasmuch as changes therein may bemade without the exercise of invention, and within the true spirit andscope of the claims hereto appended.

In said drawing, Fig. l is a circuit diagram of a rectifying systemassembled in accordance with the principles of the present invention;and

Fig. 2 shows the relationships between the various voltages applied tothe system from the power supply.

Referring now more in detail to the aforesaid illustrative embodiment ofthe present invention, with particular reference to Fig. 1 of thedrawing, the numerals i5, H and I2 generally designate gaseous-dischargetubes, known a thyratrons, and including, respectively, cathodes l3, l4and I5, anodes l6, l1 and I8, and control grids I9, 20 and 2|.

The anodes I6, I? and I8 of said tubes I0, II and I2 are connected,respectively. to the outer terminals of secondary windings 22, 23 and 24of a multi-phase power transformer 25, the inner terminals of saidwindings being connected together and constituting a neutral referencepoint 25.

Said transformer 25 additionally includes primary windings 21, 2B and 29connected to lines 30, 3| and 32 of a three-phase, alternating-current,commercial power source, and another group of secondary windings 33, 34and 35 connected together at their inner terminals, as at a neutralreference point 355, said first and secondnamed secondary windings beingso disposed with respect to each other that the voltages developedthereacross are in phase opposition.

The anodes l6, ii and [8 of the tubes H], H and I2 are also connected,respectively, to cathodes 31, 38 and 39 of additional gaseous-dischargetubes 45, i! and 42, said last-named tubes including anodes d3, 44 and45 connected to ground, as at 46, and, through a load resistor 41,lay-passed by a capacitor 58, to the cathodes l3, l4 and 15, of saidfirst-named gaseous-discharge tubes.

Said cathodes I3, I41 and i5 of said tubes III, II and 12 are alsoconnected, through a bias resistor 49, by-passed by a capacitor 50, tothe neutral point 35 of the second above-mentioned secondary windings33, 34 and 35, and, through contacts 5| and 52 of a ganged switch 53,and a resistor 54 and relay 55, to ground, as at 56. The

3 r eglay 55 controls contacts in the lines 30, an and I) The outerterminals of the secondary windings 33, 3d and 35 are connected,respectively, through resistors 57, 50 and 59, to one of the endterminals 50, 65 and 62 of potentio-meters 63, 05 and t5, the remainingend terminals 65, 6? and 68 of said potentiometers being connectedrespectively, through resistors 59, i and H, to the outer terminals ofthe secondary windings 34, 35 and 33. The resistance between the endterminals of each of the potentiometers 63, 64 and is centertapped,respectively, as at l2, l3 and M, whereby said potentiometers comprise,respectively, pairs of resistors l5 and '16, TI and i8, and 19 and 00.The center taps l2, l3 and M are connected, respectively, to the outerterminals of the secondary windings 35, 33 and 34. V

By means of the potent ometer connections just described, two phases ofthe power su ply are applied to each potentiometer, and, as willhereinafter be further described, phase shifts of up to substantially240 may be obtained.

The potentiometers 63, 64 and 65 include, respectively, adjustable arms8!, 82 and 83 which are ganged together, as indicated by the brokenlines, and said adjustable arms are connected, respectively, throughpairs of series-connected resistors 051 and 05, 85 and 81, and 88 and89, to the control grids I9, 20 and 2! of the gaseousdischarge tubes 50,l l and H2. The junctions between the pairs of series-connectedresistors just described are connected, respectively, to contacts 90, stand 92 included in the switch 53. Additional contacts 03, 94 and 05,cooperable, respect vely, with the contacts 90, 9! and 92, areconnected, respectively, to the end terminals 50, 6! and 62 of thepotentiometers 53, 54 and 65.

The grids i0, 20 and 2! of the tubes l0, H and i2 are also c nnected,respectively, through capacitors 96, 91 and 98, to the cathodes I3, M-and lliof said tubes.

This completes the descr t on of the aforesaid illustrative embodimentof the invention and the mode of operation thereof will now bedescribed, for which purpose reference is made to Fig 2 of the drawingas well as to Fig. l.

. In said Fig. 2 of the drawing, there are shown three main voltages A,B, and C corresponding,

to the three phases, spaced 120 apart, of the. commerc al power lines30, 3! and 32, and three commutating voltages A, B and C, likew sespaced 120 apart, but in phase opposition, respectivelv, to saidvoltages A, B and C.

It will be assumed, for the purposes of this s ecification, that themain voltages A, B and C, which appear across the secondarv windings 22,23 and 24, have a peak value of about 5,000 volts, and that thecommutating voltages A, B and C, which a pear across the secondarywindings 33, 3d and 35, have a peak value of about 150 volts.

Consider the time 251, at which the main voltage A is somewhat greaterthan one-half its positive peak, for example, 2,550 volts; the mainvoltage B is somewhat less than its negative peak, for example, 4,950volts; and the main voltage C is somewhat less than one-half itspositive peak, for example 2,450 volts, all with respect to the neutralreference point 26. At the same time, the commutating voltage A issomewhat greater than one-half its negative peak, for example, 130

volts, all with respect to the neutral reference point 36,

Under these circumstances, the cathode 3'! of the gaseous-discharge tube40 will be positive with respect to the anode 03 of said tube, and saidtube will be non-conducting. The cathode 39 of the gaseous-dischargetube 32 will be positive with respect to the anode 5 of said tube, andsaid tube will also be non-conducting. However, the cathode 38 of thegaseous-discharge tube ii will be negative with respect to the anode Mof said tube, and said tube will be conducting.

Hence, there appears upon the anode E0 of the gaseous-discharge tube illa voltage which is 7,500 volts positive (the sum of voltages across thewindings 22 and 23) with respect to the oathode iii of said tube, andthe latter, if it were not for the fact that the instantaneous voltageon its control grid it? was 130 volts negative with respect to itscathode it, would be conducting.

There appears upon the anode iii of the gaseous-discharge tube l2 avoltage which is 7,400

' volts positive (the sum of the voltages across the windings 23 and2:3) with respect to the cathode 55 of said tube. but the control grid2d of. the latter is 120 volts negative with respect to the oath ode 5,and therefore, said tube, too, is non-con n ducting.

' ter is non-conducting, even though its control volts: the commutatingvoltage B is somewhat.

l ss than its positive peak, for example, 145 'voltsj grid 20 is 145volts positive with respect to its cathode l4.

Thus, at the time t1, none of the gaseous-discharge tubes :10, ii and i2 is conducting, and consideration of the voltage relationships at anytime within the 360 illustrated in Fig. 2 of the drawing will reveal thesame non-conducting conditions, these conditions obtaining as long asthe commutating voltages A. B and C are maintained 180 out of phase withthe main voltages A, B and C. The potentiometers 63, M and 65, and thevar-- ious re istors between sa d potentiometers and the ga eous-dcharge tubes In, H and i2 and the secondary wind ngs and 35, preferably,are of such values that when the adjustable arms at. 82 and 83 of saidpotentiometers are in their extreme counter-clockwise positions, theout-ofphase relation h ps above referred to exists.

Now, assume that the adjustable arms 0!, 02 and 83 of the potentiometersE3. 6 and 65 are moved, in a clockwise d rection. to advance the pha eof the commutating voltages, each, Further assume that the commutatingvoltages are now represented by the sine waves A, B

and C" in Fig. 2 of the drawing, and consider the time t2.

At said time 152. the main voltage A is at its po itive peak, 5.000volts: and the main voltages B and C are each at one-half their negativepeak, 2,500 volts, the former becoming less negative, and the latterbecoming more negative. At the same instant. the commutating voltage Ais zero, but starting on its positive alternation; the" commutatingvoltage B" is somewhat less than its negative peak. for example, volts;and' the commutating voltage C is somewhat less than po itive peak, forexample, '145 volts.

Under these circumstances, the cathode s! or the gaseous-discharge tube40 is positive -with respect to the anode 33 of said tube, and said tubewill be non-conducting. The cathode 3B of the gaseous-discharge tube Mwill, until the point of the cross-over between the main voltages B andC is reached, be negative with respect to the anode M of said tube, anduntil said cross-over point is reached, said tube will be conducting. Assoon as said cross-over point is passed, the cathode 3g of the tube 4!will be positive with respect to the anode 4c of said tube, and saidtube will no longer conduct. The cathode 39 of the gaseous-dischargetube 42 will, until the above-referred to cross-over point is reached,be positive with respect to the anode A5 of said tube, and until saidcross-over point is reached, said tube will be non-conducting. As soonas said cross-over point is passed, the cathode 39 of the tube 42 willbe negative with respect to the anode 45 of said tube, and said tubewill begin to conduct.

Hence, there appears upon the anode 15 of the gaseous-discharge tube It!a voltage which is '7 500 volts po itive (the sum of the voltages acrossthe windings 22 and 24) with respect to the oathode [3 of said tube, andinasmuch as the commutating voltage A is, at the instant underconsideration, going positive, said tube ID will begin to conduct.

Now, during the periods that no one of the tubes il I! and i2 isconducting, the potential of the cathodes 13, M and 15 of said tubesfollows the lower envelope of the voltages A, B and C, but as soon asany one of said tubes becomes conducting, said cathodes attain apotential equal to the potential of the anode of the instantaneouslyconducting tube minus the small drop wi hin said conducting tube itself.

Therefore, as soon as the tube ll) becomes conducting as aforesaid,there appears upon the anode i! of the gaseous-discharge tube H avoltage which is somewhat less than 7,504 volts negative with respect tothe cathode M of said tube i l, and said tube will not conduct.Actually, the control grid 28 of said tube I! is, at this instant, about145 volts negatve with respect to the cathode H thereof.

There appears upon the anode !8 of the gaseons-discharge tube [2 avoltage which is, at the instant under consideration. somewhat more than7,590 volts negative with respect to the cathode 15 of said tube, andtherefore, even though the control grid 2i of said tube is about 145volts positive with re pect to said cathode 55, said tube 52 will notconduct.

Now, once the tube H] is conducting, it will continue to conduct untilits anode potential goes negative with respect to its cathode. Thiswould not occur until time 253 were reached if it were not for thecapacitor 48. The residual voltage across said capacitor 48 causes thisto occur, actually, at some short time before the time is.

At that time, the anode and control grid volttages of thegaseous-discharge tube i I will be the same as the anode and controlgrid voltages of gaseous-discharge tube ll! were at the time t2.Therefore, the tube I! will start to conduct, the cathodes l3, :4 and 15will jump almost to the tial of the anode ll of said tube H, and in 3hthis potential is positive with respect to anode Hi of the tube 55, thelatter will cease conducting.

i. he same sort of commutation will occur shortly before time 154, whenthe gaseous-discharge tube if: will start to conduct and thegaseous-discharge tube it will stop conducting.

As each tube !0, II and i2 conducts, current will flow through the loadresistor 41, said current producing the output voltage of the system.

With a phase shift of such as has been under consideration in theforegoing description, tubes i9, 5 I and 12 will conduct for the periodsindicated by the shaded portions, respectively, from left to right,superimposed on the sine waves A, B and C. As indicated in earlierportions of this specification, the magnitude of the phase shiftintroduced by adjustment of the ganged potentiometer arms 8!, 32 and 83will control the duration of the conducting intervals of the tubes H3,Ii and I2, and, in turn, the duration of said time intervals willcontrol the average output voltage developed across the load resistor48.

The ganged switch 53 enables the output voltage to be tuned. on and offwithout regard to the magnitude thereof, and the relay 55 is utilized toautomatically open the power lines in the event said switch 53, whenclosed, fails to reduce the output voltage substantially to zero.

This completes the description of the mode of operation of the aforesaidillustrative embodiment of the present invention.

It will be noted from all of the foregoing that the present inventionprovides a rectifying system for a multi-phase, alternating-currentpower supply, especially, a rectifying system which includes thyratrons,in which there is incorporated a simple and efficient means forobtaining continuously variable output voltage. It will further be notedthat the rectifying system of the present invention is so designed as toprevent the same from being damaged by excessive inverse voltages of thepower supply.

Other objects and advantages of the present invention will readily occurto those skilled in the art to which the same relates.

What is claimed is:

l. A rectifying system for a multi-phase, altermating-current powersupply comprising: a plurality of gaseous-discharge tubes each of whichincludes a cathode, an anode, and a control grid; a plurality ofadditional gaseous-discharge tubes each of which includes a cathode andan anode; said first and second-named gaseous-discharge tubes beingconnected, respectively, in series with each other; means adapted to beenergized from said power supply, for applying such potentialdifferences between the anodes and cathodes, and the control grids andcathodes of said first-named gaseous-discharge tubes, and between theanodes and cathodes of said second-named gaseous-discharge tubes as tomaintain said first-named tubes initially non-conducting; a loadimpedance connected across said series-connected, first and second-namedgaseous-discharge tubes; resistance networks connected in series withthe potential difference applied between the control grids and cathodesof said first-named gaseous-discharge tubes, for so shifting the phaseof said potential difference as to render said gaseous-discharge tubessuccessively conducting, each for a time interval which is a function ofthe magnitude of said phase shift; and means across which control-gridrectification develops a bias sufficient to maintain all but one of saidfirst-named gaseous-discharge tubes. non-conducting; the current flowingas a result of the conducting state of each of said first-namedgaseous-discharge "ubes developing an average potential across said loadimpedance the magnitude of which is a function of the duration of saidtime interval.

2. A rectifying system for a multi-phase, alterhating-current powersupply comprising: a plurality of gaseous-discharge tubes each of whichincludes a cathode, an anode, and a control grid; a plurality ofadditional gaseous-discharge tubes each of which includes a cathode andan anode; said first and second-named gaseous-discharge tubes beingconnected, respectively, in series with each other; means, adapted to beenergized from said power supply, for applying such potentialdifferences between the anodes and cathodes, and the control grids andcathodes of said firstnamed gaseous-discharge tubes, and between theanodes and cathodes of said second-named gasecue-discharge tubes as tomaintain said firstnarned tubes initially non-conducting; a loadimpedance connected across said series-connected, first and second-namedgaseous-discharge tubes; resistance networks connected in series withthe potential diiference applied between the control grids and cathodesof said first-named gaseousdischarge tubes, for so shifting the phase ofsaid potential difference as to render said gaseousdischarge tubessuccessively conducting, each for a time interval which is a function ofthe magnitude of said phase shift; and a resistance capacitance networkacross which control-grid REFERENCES CITED The following references areof record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,829,254 Asch Oct. 27, 19311,874,840 Williamson Aug. 30, 1932 2,037,567 Ehrensperger et al. Apr.14:, 1936 2,085,940 Armstrong July 6, 1937 2,093,329 Lord Sept. 14, 19372,103,996 Bedford Dec. 28, 1937 2,137,126 Bedford Nov. 15, 19382,288,338 Willis June 30, 1942

